Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$247.45	4.515%	$258.6224	$258.62	$258.60	$258.60
Purchase #2	$166.43	13.479%	$188.8631	$188.86	$188.85	$188.90
Purchase #3	$234.25	10.171%	$258.0756	$258.08	$258.10	$258.10
Purchase #4	$92.47	12.801%	$104.3071	$104.31	$104.30	$104.30
Purchase #5	$210.40	10.571%	$232.6414	$232.64	$232.65	$232.60
Purchase #6	$96.67	8.263%	$104.6578	$104.66	$104.65	$104.70
Purchase #7	$148.81	13.378%	$168.7178	$168.72	$168.70	$168.70
7 purchase totals =	$1,196.48		$1,315.8852	$1,315.89	$1,315.85	$1,315.90